Looks like whoever did that used conventional oil for the 15,000 mile changes.
There is a guy on the BMW E90 3-series forums with over 330,000 miles on a 2006 325i. It has had BMW synthetic 5w30 it's whole life and the engine is very clean inside. Most changes were using the oil monitor for OCI between 15,000-17,000 miles.
With that said, we all know how important it is for the car to get to operating temp, and a quality synthetic oil to be used. My guess is this person used conventional or short tripped.
My OCD would still have me changing the oil earlier than the monitor on an engine as expensive as that one though.